The invention relates in general to gas handling systems for semiconductor processing and in particular, to gas panel systems whether of a localized nature or distributed around a semiconductor processing tool.
Wafer fabrication facilities are commonly organized to include areas in which chemical vapor deposition, plasma deposition, plasma etching, sputtering and the like are carried out. In order to carry out many of these processes, it is necessary that the tools which are used for the process, be they chemical vapor deposition reactors, vacuum sputtering machines, plasma etchers or plasma enhanced chemical vapor deposition, be supplied with various process gases which gases may be reactive or inert or provide reactive species.
For instance, in order to perform epitaxial deposition, silicon tetrachloride has bubbled through it a carrier gas such as dry nitrogen, which then carries silicon tetrachloride vapor into an epitaxial deposition chamber. In order to deposit a silicon oxide dielectric coating, also known as a deposited oxide coating, silane (SiH4) is flowed into the tool and oxygen is flowed into the tool where they react to form (SiO2) on the surface of the wafer. Plasma etching is carried out by supplying carbon tetrachloride and sulfur hexafluoride to a plasma etcher tool. The compounds are ionized, to form reactive halogen species which then etch the silicon wafer. Silicon nitride may be deposited by the reaction of dichlorosilane and ammonia in a tool. It may be appreciated that in each instance pure carrier gases or reactant gases must be supplied to the tool in contaminant-free, precisely metered quantities.
In a typical wafer fabrication facility the inert and reactant gases are stored in tanks which may be located in the basement of the facility and which are connected via piping or conduit to a valve manifold box. The tanks and the valve manifold box are considered to be part of the facility level system. At the tool level an overall tool system, such as a plasma etcher or the like, includes a gas panel and the tool itself. The gas panel contained in the tool includes a plurality of gas paths having connected therein manual valves, pneumatic valves, pressure regulators, pressure transducers, mass flow controllers, filters, purifiers and the like. All have the purpose of delivering precisely metered amounts of pure inert or reactant gas from the valve manifold box to the tool itself.
The gas panel is located in the cabinet with the tool and typically occupies a relatively large amount of space, as each of the active devices are plumbed into the gas panel, either through welding tubing to the devices or combinations of welds and connectors such as VCR connectors available from Cajon Corporation or the like.
Gas panels are relatively difficult to manufacture and hence expensive. In a combination VCR connector and welded tubing system the individual components are held on shimmed supports to provide alignment prior to connections at VCR fittings. Misalignment at a VCR fitting can result in leakage.
In addition, it has been found that VCR fittings often tend to come loose in transit and some gas panel manufacturers assume that the VCR fittings have loosened during transit, possibly admitting contaminants to the system.
Welds are relatively expensive to make in such systems but are typically carried out using a tungsten inert gas (TIG) system, having an orbital welding head to weld a tube stub and a tube together. The welding must take place in an inert atmosphere, such as argon, and even then leads to deterioration of the surface finish within the tubes. One of the important characteristics of modern-day gas panel systems and gas handling systems is that the surfaces of the gas handling equipment that tend to have the gas or vapor contact them must be made as smooth and nonreactive as possible in order to reduce the number of nucleation sites and collection sites where contaminants may tend to deposit in the tube, leading to the formation of particulates or dust which would contaminate the wafers being processed.
Additional problems with conventional gas panels relate to the fact that a combination VCR and welded system of the type currently used today typically requires a significant amount of space between each of the components so that during servicing the VCR connections can be accessed and opened. In addition, in order to remove an active component from a contemporary gas panel, many of the supports of the surrounding components must be loosened so that the components can be spread out to allow removal of the active component under consideration.
Most wafer fabricators are aware that it is only a matter of time until, for instance, the silane lines in the gas panels are xe2x80x9cdusted.xe2x80x9d xe2x80x9cDustingxe2x80x9d occurs when air leaks into an active silane line causing a pyrophoric reaction to take place yielding loose particulate silicon dioxide in the tube, thereby contaminating the line. Other lines also can be contaminated. For instance, those which carry chlorine gas used in etchers or which carry hydrogen chloride used in other reactions. Hydrogen chloride mixing with moisture present in the humidity of air produces hydrochloric acid which etches the interior of the tube, roughening it and increasing the number of nucleation sites and the likelihood that unwanted deposition would occur inside the tube. In both of these cases, as well as in others, it would be necessary then to open the particular line in the gas panel in order to clean it.
In addition, individual component failures may require a line being opened in order to clean it and is time consuming and expensive.
What is needed, then, is a view type of gas panel which is compact, inexpensive to manufacture and easy to service.
In accordance with the present invention, a gas panel assembly is provided including a plurality of active device receiving one-piece gas or vapor manifolds. The active device receiving manifolds are arranged so that they receive gas or vapor at an inlet end, pass the gas or vapor along to a plurality of interior channels to a plurality of active device receiving stations which may be connected to an active device or have connected thereto a gas return cap and ultimately deliver the gas or vapor from an outlet for ultimate supply to a tool.
The inventive gas panel assembly is easy to manufacture, in that a standardized manifold is used with a standardized footprint for connection to the active devices. Each of the active device sites is positioned along the face of the substantially rectangular manifold and is oriented to extend at substantially right angles to, the face of the active device manifold and therefore out of the general flow path. Each of the devices is connected to the manifold by a plurality of Allen-head bolts which hold the device base onto the manifold and which may be quickly and easily removed in order to remove a particular device from the system without disturbing other portions of the system.
The manifolding system is also self-aligning, in that each manifold is a repeatable machined component which has been prefabricated. There is no necessity either to provide welded connections or VCR and tube connections directly to the active devices as the connections are made through and support provided by the manifold itself. By tucking within the manifold each of the inlet and outlet connection loops from the manifold between adjacent stations, this greatly saves space and allows a great reduction in the amount of space over that required by a prior gas panel assembly.
The gas panel assembly embodying the present invention is easy to manufacture in that each of the active devices is separately aligned. If misalignment were to occur, for instance, between a pressure regulator and the device receiving station on the surface of a one-piece manifold, an adjacent valve mass flow controller or the like would not be positioned out of alignment with the general manifolding structure as a result thereof. Thus, any misalignment which may occur has been uncoupled from neighboring stations through the use of the manifolding system. Tolerance stack-up problems are also avoided by the simultaneous ability of the manifold to connect with and register the active devices.
Each of the active devices which are connected to the manifold may be prefabricated in that they include a combination seal and screw capture mechanism component, the seal including a keeper for holding the seal in alignment with the active device and the screws being held captured by nylon split rings to hold the screws within the bores of the active device mount. This allows for quick and easy assembly. The active devices are seated upon edge seals at the active sites. The edge seals do not require extensive or fine surface preparation yet provide good, leak-free and contaminant-free joins at the gas flow inlets and outlets between the manifold and the active devices. The seals are easily removable for replacement during repair. They include keepers for self-locating which is particularly helpful when replacing an active device on a manifold face in the field.
The inventive gas panel manifold system also allows an entire manifolding assembly, or stick, to have applied thereto heated tape or other types of heaters in order to heat all of the manifold bores extending among..the active device components and maintain a low vapor pressure gas or vapor in a vapor state throughout each of the process gas lines of the system.
The inventive gas panel manifolding system allows the gas panel to be easily reconfigured by a user in the field as welds and VCR connections need not be broken. An active device may be replaced or added simply by lifting it out of connection with an active device site and a new one connected thereto.
A pair of nitrogen purge inlets is provided, both at the upstream and the downstream end of the one-piece manifolds so that should it be necessary to remove an active device from the manifold, dry nitrogen can be blown both backward and forward through the manifold. Dry, clean nitrogen would exit at both the exposed inlet and outlet ports the active device site and contamination of the rest of the manifold during the course of the changing of the active device site be eliminated.
In addition, in a particular embodiment of the present invention the manifolded gas panel system includes pressure transducers having visual digital readouts so that the pressure can be directly viewed by an operator at the site as well as transmitted to a control computer.
In an additional feature of the present device, the gas panel system is enclosed within a gas panel housing having a floor, sides and a cover. Extending across the floor of the gas panel housing is a plurality of threaded mounts adapted to engage mounting apertures in the ends of each of the gas panel manifolds. The mounts allow the upper surfaces of the manifold, which receive the active devices, to be individually aligned into a single plane. This allows a rapid assembly of active devices across the gas panel system and allows bridging connectors to be easily aligned with the overall gas panel active device plane defined by each of the manifolds. The single device plane construction also provides easy access to the Allen head bolts holding the active devices to the manifolds.
U-tube type bridge connectors, having long-connector legs and short cross tubes connected together by Cajon elbows for interconnecting successive manifolds to bridge various manifolds, provide a route for purge gas, such as nitrogen. The long tubing provides mechanical advantage allowing limited flexure of the short bridging tube. The U-tube connection is thus dimensionally forgiving for any slight misalignment which may occur in the horizontal plane defining the active device surfaces. It may also be appreciated that a snug fit is not provided between the threaded support fasteners and the active device manifolds to allow a slight amount of horizontal play between the manifolds for easy U-tube connection therebetween. The U-tube may also be formed by bending a tube into a U-shaped configuration which would avoid the necessity of welding.
The ability to suspend the manifolds above the surface of the gas panel enclosure allows circulation of purge and vacuum air around assemblies. Many building codes for wafer fabrication facilities require prescribed amounts of purge air to sweep leaked process gas out of the housings of the gas panels for safe disposal. The improved sweep provided by the suspension of the manifolding assemblies above the floor aids in the isolation of any leaks which may occur within the gas panel system from the wafer fabrication operators.